KR101475681B1 - Use of aqueous guanidinium formate solutions for the selective catalytic reduction of nitrogen oxides in exhaust gases of vehicles - Google Patents

Abstract

The invention relates to the use of aqueous guanidinium formiate solutions, optionally combined with urea and/or ammonia and/or ammonium salts, for the selective catalytic reduction of nitrogen oxides using ammonia in exhaust gases of vehicles. The inventive guanidinium formiate solutions enable a reduction of the nitrogen oxides by approximately 90%. Furthermore, said guanidinium formiate solutions can enable an increase in the ammonia forming potential from 0.2 kg, corresponding to prior art, up to 0.4 kg ammonia per liter of guanidinium formiate, along with freezing resistance (freezing point below -25° C.). The risk of corrosion of the inventive guanidinium formiate solutions is also significantly reduced compared to that of solutions containing ammonium formiate.

Description

 Use of an aqueous solution of guanidinium formate for the selective catalytic reduction of nitrogen oxides in the exhaust gas of a vehicle.

The present invention relates to the use of an aqueous solution of guanidinium formate for the selective catalytic reduction of nitrogen oxides in exhaust gases of automobiles, wherein said guanidinium formate solution produces ammonia by evaporation and catalytic cracking, Acts as a reducing agent for subsequent selective catalytic reduction of nitrogen oxides.

According to the prior art, ammonia (NH ₃ ) acts as a reducing agent in the selective catalytic reduction (SCR) of nitrogen oxides in automotive exhaust gases and into exhaust lines of combustion systems and internal combustion engines, Into a group of SCR catalyst modules that can flow upstream or in parallel with a particular SCR catalyst and can be incorporated into a muffler to cause the reduction of nitrogen oxides present in the exhaust gas in the SCR catalyst. SCR means selective catalytic reduction of nitrogen oxides (NO _x ) in the presence of oxygen.

Various liquid and solid ammonia precursor materials for the production of ammonia, especially in vehicles, have long been known and are described in detail below.

In a utility vehicle, it has been established to use the eutectic aqueous solution of urea in water (AdBlue ^TM ) with an ammonia-forming potential of -11 캜 and a freezing point of -11 캜 with an element content of 32.5% by weight as the ammonia precursor material. For operation of the SCR system at temperatures up to -30 ° C, ie at temperatures up to the cold flow plugging point (CFPP, lower operating temperature) of winter quality diesel fuel, The relatively complicated additional heating of tanks, lines and valves is needed for Adblue use and Adblue logistics in cold winter climates.

Ammonia required for the catalytic reduction of NO _x is formed in the thermal decomposition of the urea. For this purpose, the following reaction is appropriate: the element decomposes without being evaporated upon heating, providing mainly isocyanic acid and ammonia (NH ₃ ) according to formula [1].

(H ₂ N ₂ ) CO → HNCO + NH ₃ [1]

Isocyanic acid can be easily polymerized with a nonvolatile material such as cyanuric acid. This can result in destructive deposits on the valve, on the injection nozzle, and in operation in the exhaust pipe.

Isocyanic acid (HNCO) is hydrolyzed to ammonia (NH ₃ ) and carbon dioxide (CO ₂ ) in the presence of water according to the formula [2].

HNCO + H ₂ O → NH ₂ + CO ₂ [2]

Reaction [2] proceeds very slowly in the gas phase. In contrast, the metal oxide and / or zeolite catalyst proceeds very rapidly and progresses somewhat more slowly in the metal oxides catalysts of the WO ₃ content of the resultant strong acid, such as SCR catalysts based on mixed oxides of vanadium oxide, tungsten oxide and titanium oxide do.

In the known application of element-SCR catalytic systems connected to automobiles, engine exhaust gases are generally used to utilize their heat content for pyrolysis of the elements according to reaction [1]. In principle, reaction [1] may proceed initially, such as upstream of the SCR catalyst, while reaction [2] must be catalytically accelerated. In principle, reactions [1] and [2] can also proceed on the SCR catalyst, and the activity of the SCR catalyst is consequently reduced.

For countries in cold climates, it is advantageous to be able to use freezeproof ammonia precursor materials. The addition of ammonia formate to the urea solution in water significantly lowers the freezing point. This makes additional heating unnecessary and achieves significant savings in manufacturing and logistics costs. Solutions of 26.2% and 20.1% of the ammonia formate in water have a freezing point of -30 ° C and are commercially available under the trade name Denoxium 30 and can be advantageously substituted for AdBlue ^™ in the cold season (SAE technical papers 2005-01 -1856).

The addition of ammonium formate to the urea solution in water causes the ammonia formation potential to increase from 0.2 kg / kg to 0.3 kg / kg in the case of 35% ammonium formate and 30% urea solution in water. This increases the reach of the vehicle by half as much as a single charge of the ammonia precursor material and generally provides a long-term possibility of charging between check intervals in the van. One disadvantage of this measure is that the freezing point of the solution rises in the range of -11 to -15 [deg.] C (Denoxium January 2005, www.kemira.com ).

EP 487,886 A1 proposes a process for the quantitative decomposition of ammonia (NH ₃ ) and carbon dioxide (CO ₂ ) by hydrolysis of an aqueous solution of urea in water at a temperature range of 160 to 550 ° C, Lt; / RTI > acid and its solid conversion product. In this known method, the urea solution is first sprayed by a nozzle onto an evaporator / catalyst existing inside or outside the exhaust gas. For post-treatment, the formed gaseous product passes over the hydrolysis catalyst to achieve quantitative formation of ammonia.

EP 555,746 Al discloses a method in which an evaporator uniformly distributes urea solution due to its structure to ensure contact of the liquid droplets with the channel walls of the decomposition catalyst. A uniform distribution prevents adhesion of the catalyst phase and reduces slippage of the excess reducing agent. Element metering should only be activated at exhaust temperatures from 160 ° C, since undesirable deposits form when temperatures are lower.

Conversion of ammonium formate to ammonia as an ammonia precursor material is possible by simple sublimation without any particular pretreatment by spraying the aqueous solution into hot exhaust gas. The disadvantage is the simultaneous release of highly corrosive formic acid and the ammonium formate can be reformed on the surface of the SCR catalyst at an exhaust gas temperature below 250 ° C. The pore system of the SCR catalyst is blocked in a thermally reversible manner.

It is therefore an object of the present invention to provide a process for the preparation of NO _x Level ammonia that is technically simple for reducing ammonia and does not form any unnecessary byproducts in the decomposition.

This object is achieved by using an aqueous solution of guanidinium formate for selective catalytic reduction of nitrogen oxides in automotive exhaust with ammonia in accordance with the present invention. Preferably, according to the present invention, a guanidinium formate aqueous solution is optionally used in combination with urea and / or ammonia and / or ammonia salts.

This is because, surprisingly, it has been found that the guanidinium formate used according to the invention has a higher ammonia-forming potential than the prior art. Moreover, the corresponding aqueous solutions of guanidinium formate can be evaporated in a technically simple manner and no solid decomposition products are formed, possibly in the exhaust gas system, which can lead to encrustation and blockage.

For the selective catalytic reduction of nitrogen oxides in oxygen-containing or anoxic exhaust gases of automobiles with ammonia, according to the invention, an aqueous solution of guanidinium formate is used, which is preferably a solid (guanidinium formate content) 85% by weight, in particular from 30 to 80% by weight and preferably from 55 to 60% by weight and optionally in combination with urea and / or ammonia and / or ammonium salts. Although it has been found that it is particularly advantageous to have a mixture of guanidinium formate and urea having 5 to 60 wt% guanidinium formate content and 5 to 35 wt%, especially 10 to 30 wt% urea content, The mixing ratio of formate to urea and ammonia or ammonium salt may vary within a wide range. It is also believed that a mixture of guanidinium formate and ammonia or ammonium salts having 5 to 60% by weight of guanidinium formate and 5 to 40% by weight of ammonia or ammonium salts is preferred.

The aqueous solution used according to the invention has a water content of ≥ 5% by weight, preferably ≥10% by weight, based on the total weight of the solution. The water is preferably at least the main solvent having a ratio of? 50 wt%, preferably? 80 wt%, more preferably 90 wt%, based on the total weight of the solvent in the single solvent or solution.

It has been found that the ammonium salt useful in this context is specifically a compound of the general formula (I).

      (I)

Wherein R = H, NH ₂ or C ₁ -C ₁₂ alkyl,

       X = acetate, carbonate, cyanate, formate, hydroxide, methoxide or oxalate.

It is contemplated that the guanidinium formate aqueous solution and, if appropriate, additional components are subject to catalytic decomposition by ammonia in the preferred temperature range of 150 to 350 DEG C, and the additional components formed are carbon dioxide and optionally carbon monoxide . The decomposition of guanidinium formate into ammonia can be carried out in the presence of an oxide selected from the group of titanium dioxide, aluminum oxide and silicon dioxide and mixtures thereof and / or oxides of completely or partially metal-exchanged hydrothermally stable zeolites, in particular ZSM 5 or BEA type There is a catalytic activity of the iron zeolite and is carried out in the presence of an oxidation-inactive coating. Useful metals here are especially transition elements and are preferably iron or copper. The corresponding Fe zeolite material is prepared by known methods, for example by solid phase exchange, for example by solid phase exchange with FeCl ₂ , then in the form of a slurry on a substrate (for example cordierite monolith) Or at high temperature (approximately 500 ° C).

Metal oxides such as titanium oxide, aluminum oxide and silicon dioxide are preferably applied to metal carrier materials, for example thermoelectric alloys (especially chromium-aluminum steels).

The guanidinium formate solution or the remaining components may also be catalytically decomposed with ammonia and carbon dioxide, in this case oxides selected from the group of titanium dioxide, aluminum oxide and silicon dioxide and mixtures thereof, and / or oxides of totally or partially A catalytically active coating of a metal-exchanged hydrothermally stable zeolite is used, the coating being impregnated with gold and / or palladium which is an oxidation-active component. The corresponding catalyst comprising palladium and / or gold as the active component preferably has a noble metal content of from 0.001 to 2% by weight, in particular from 0.01 to 1% by weight. With the aid of such an oxidation catalyst, it is possible to prevent the formation of undesired carbon monoxide as a by-product in the decomposition of guanidine salt initially during the ammonia production process.

Preferably, for catalytic cracking of guanidinium formate and, if appropriate, further components, a catalytic coating is used which comprises palladium and / or gold as the active component in a content of noble metal from 0.001 to 2% by weight, in particular from 0.01 to 1% by weight .

It is possible in the context of the present invention that a catalyst consisting of two parts is used, the first part comprising an oxidation-inactive coating and the second part comprising an oxidation-active coating. Preferably, 5 to 90% by volume of the catalyst consists of 10 to 95% by volume of an oxidation-inactive coating and an oxidation-active coating. Alternatively, the catalytic cracking may also be carried out in the presence of two catalysts arranged in series, in which case the first catalyst comprises an oxidation-inactive coating and the second catalyst comprises an oxidation-active coating.

The catalytic cracking of the guanidinium formate used according to the invention into ammonia or the catalytic cracking of the guanidinium formate used according to the invention and of the further constituents into ammonia is carried out in the presence of an exhaust gas By catalytic cracking in the exhaust stream in a main stream, a partial stream or a secondary stream, or by autobaric and extraneously from the outside of the exhaust gas system, ) Catalytic cracking in the heated arrangement.

The present invention also relates to an aqueous composition comprising guanidinium formate having a concentration of 5 to 85% by weight, preferably 30 to 80% by weight, optionally in combination with urea and / or ammonia or ammonium salts, As a means for selective catalytic reduction of nitrogen oxides in automotive exhaust gases. The mixture of guanidinium formate and urea preferably has a guanidinium formate content of 5 to 60% by weight and an urea content of 5 to 35% by weight. The mixture of guanidinium formate and ammonia or ammonium salt preferably has 5 to 60% by weight of guanidinium formate and 5 to 40% by weight of ammonia or ammonium salt.

With the aid of the proposed guanidinium formate aqueous solution proposed in accordance with the invention, it is possible to achieve a reduction of the level of nitrogen oxides in the exhaust gas of the vehicle by approximately 90%. In addition, with the guanidinium formate solution proposed in accordance with the present invention, increasing the ammonia-forming potential of 0.2 kg of ammonia per liter of guanidinium salt according to the prior art up to 0.4 kg has the advantage of achieving winter stability (below freezing point -25 캜) It is possible to have at the same time. Finally, the risk of corrosion of the guanidinium formate solution used in accordance with the present invention is also significantly reduced compared to solutions containing ammonium formate.

The following examples are intended to illustrate the present invention in detail.

1 is a schematic view of a process for selectively catalytically reducing nitrogen oxides in automobile exhaust gas.

Example  One

The use of 40 wt% guanidinium formate aqueous solution (GF) (m.p. -20 < 0 &gt; C) as the ammonia precursor material in the automatic pressure-

The automotive engine 1 produces an exhaust gas stream of 200 m ³ (STP) / h which passes over the platinum oxidation catalyst 3 and the particulate filter 4 through the intermediate pipe 2, (6). The exhaust gas composition measured by the FTIR gas analyzer 5 in the intermediate tube 6 was: nitrogen oxide, NO 150 ppm; Nitrogen dioxide, N0 ₂ 150ppm; Carbon dioxide, 7% CO ₂ ; 8% of water vapor, 10 ppm of carbon monoxide and CO.

Inside the tank vessel 7 there is a GF solution which is injected by the metering pump 9 into the reactor 11 through the feed line 10 and the nozzle 12. The reactor 11 is composed of a vertical tube heated to 250 ° C, which has an inner diameter of 51 mm and is made of austenitic steel and has a heating jacket 15. The catalysts (13) and (14) are in the reactor (11). The catalyst is a metal carrier (diameter 50 mm, length 200 mm, metal carrier manufacturer: Emitec GmbH, D-53797 Lohmar) coated with titanium dioxide from Sudchemie AG, Heufeld, Germany. Catalyst 13 is based on a coarse-cell MX / PE 40 cpsi carrier type and is 100 mm long. In the downstream direction, the catalyst 14 is composed of a fine-cell MX / PE 200 cspi carrier type having a length of 100 mm and a length of 100 mm. The end face of the rough cell catalyst 13 is sprayed from the nozzle 12 to the GF solution 8 by the pressure metering pump 9. [ The nozzles 12 are arranged upstream of the coarse-cell catalyst 13 in the axial direction of the reactor 11. The moisture content of the GF solution 8 is evaporated on the catalyst 13 and the GF is thermally-hydrocracked on the catalysts 13 and 14 to prevent the formation of urea and isocyanic acid, HNCO intermediates .

The mixture of ammonia, carbon dioxide, carbon monoxide and water vapor formed is introduced into the exhaust gas intermediate pipe 6 through the feed pipe 16 and is preheated to the catalyst 3 and the filter 4 upstream of the SCR catalyst 18 at 300 占 폚 Is introduced into the exhaust gas (200 m ³ (STP) / h) of the automobile engine 1. The administration of the GF solution (8) is controlled by a pressure metering pump (9) so that an ammonia concentration of 270 ppm can be measured with an FTIR gas analyzer (17). At the same time, there is an increase in the concentration of CO up to 90 to 100 ppm as a result of decomposition of the formate content of the GF solution (8). As expected, the increase in CO ₂ content and water vapor content as a result of the evaporation and decomposition of the GF solution 8 is low and almost impossible to measure. The catalytic hydrolysis of the GF is completed because the isocyanate, HNCO, can not be detected by the gas analyzer 17, and the attachment of the urea and its decomposition products can not be detected.

Downstream of the SCR catalyst 18, the FTIR gas analyzer 19 measures the reduction of the NO and NO ₂ concentration by as much as 30% up to 30 ppm. Simultaneously, the reaction of ammonia, NH ₃ with NO and NO ₂ is completed to produce nitrogen and N ₂ . The ammonia concentration at the downstream of the SCR catalyst 19 is < 2 ppm.

The FTIR analyzers 5, 17, and 19 enable exhaust gas analysis of the components NO, NO ₂ , CO, CO ₂ , H ₂ O, ammonia, NH ₃ , and isocyanic acid, HNCO components simultaneously.

Example  2

The procedure is similar to that of Example 1 except that the titanium dioxide catalyst 14 is replaced by a palladium oxide-titanium dioxide catalyst, which is impregnated with an aqueous Pd (NO ₃ ) ₂ solution and dried and calcined 5 hours) to form a catalyst containing 1 wt% PdO (= about Pd 0.9 wt%), which causes partial oxidation of carbon monoxide. The CO concentration increase could not be measured by the FTIR analyzer (17).

Claims (17)

An aqueous solution for use in selective catalytic reduction of nitrogen oxides in automotive exhaust with ammonia, said aqueous solution comprising guanidinium formate, or said aqueous solution comprising an additional component selected from urea, ammonia and ammonium salts, Formate. &Lt; / RTI &gt; The aqueous solution according to claim 1, having a guanidinium formate content of 5 to 85% by weight. The aqueous solution according to claim 1, comprising a mixture of guanidinium formate and urea having a guanidinium formate content of 5 to 60 wt% and an urea content of 5 to 35 wt%. The aqueous solution according to claim 1, characterized in that it comprises a mixture of guanidinium formate and ammonia or ammonium salt, wherein the guanidinium formate content is from 5 to 60% by weight and the ammonia or ammonium salt content is from 5 to 40% . The aqueous solution according to claim 1, wherein the ammonium salt is a compound represented by the general formula (I)

(I) here, R = H, NH ₂ or C ₁ -C ₁₂ alkyl, X ^- = acetate, carbonate, cyanate, formate, hydroxide, methoxide or oxalate. The method of claim 1, wherein said guanidinium formate or said guanidinium formate and said additional component are selected from the group consisting of a main stream, a partial stream, or a secondary stream Or by catalytic cracking in an auto-pressurized and externally heated arrangement external to the exhaust gas system. &Lt; RTI ID = 0.0 &gt; [0002] &lt; / RTI &gt; 7. The process of claim 6, wherein the catalytic cracking of the guanidinium formate with and without carbon monoxide, ammonia and carbon dioxide is carried out in the presence of ammonia and carbon dioxide, either with the carbonyloxide of the guanidinium formate and the further component, And catalytic cracking to carbon dioxide is carried out in the presence of a catalyst-active oxidation-inactive coating, wherein the catalyst-active oxidation-inactive coating comprises at least one oxide selected from the group consisting of titanium dioxide, aluminum oxide and silicon dioxide Or the catalyst-active oxidation-inactive coating comprises at least one zeolite completely or partially metal-exchanged, or wherein the catalyst-active oxidation-inactive coating comprises titanium dioxide, aluminum oxide and silicon dioxide At least one kind of oxide selected from the group consisting of In-comprising a mixture of at least one zeolite exchanged, the catalyst-active oxide-inert coating is an aqueous solution, characterized in that present in the form which is supported on a carrier. 7. The process of claim 6 comprising, for the catalytic cracking of the guanidinium formate or of the further components with ammonia and carbon dioxide, an oxide selected from titanium dioxide, aluminum oxide and silicon dioxide, a metal zeolite, or mixtures thereof Wherein the catalyst-active coating is impregnated with at least one of gold and palladium as an oxidation-active component, the catalyst-active coating being present in the form of being supported on a carrier Aqueous solution. 7. The process of claim 6, wherein a catalyst coating having at least one of palladium and gold as the active ingredient at a noble metal content of 0.001 to 2% by weight is obtained by catalytic cracking of the guanidinium formate, Characterized in that it is used for the catalytic cracking of further components, said catalyst coating being in the form of being supported on a carrier. 7. The method of claim 6, wherein a catalyst consisting of a first portion and a second portion is used, wherein the first portion comprises an oxidation-inactive coating and the second portion comprises an oxidation-active coating, Wherein the oxidation-active coating is present in the form of being supported on a support. 11. The aqueous solution according to claim 10, wherein 5 to 90% by volume of the catalyst consists of an oxidation-inactive coating, and 10 to 95% by volume of the catalyst comprises an oxidation-active coating. 7. The method of claim 6, wherein the catalytic cracking is carried out in the presence of a first catalyst and a second catalyst arranged in series, the first catalyst comprising an oxidation-inactive coating, . The aqueous solution according to claim 1, wherein the catalytic decomposition of the aqueous solution is carried out at 150 to 350 ° C. The aqueous solution according to claim 2, having a guanidinium formate content of 30 to 80% by weight. delete delete delete

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